1. Field of the Invention
The invention relates to shock absorbers and more particularly to arrangements for bringing about different kinds of damping characteristics in a shock absorber.
The damping characteristics are determined by controls, independently of variations in any parameter which seeks to change the set damping effects, in an undesirable manner. For example, such a parameter might be constituted by the shock absorber's piston speed, which causes a speed dependent variation. The shock absorber comprises a piston/piston rod working in a fluid medium in the cylinder of the shock absorber. Moreover, the shock absorber works with a servo function, in which a first valve element carries out a determination of the size of a restriction in a principal medium flow between the upper and lower sides of the piston depending on a first pressure produced by means of a pilot medium flow ("pilot flow") running between the upper and lower sides which is determinable with a second valve element that is controllable by the controls.
2. Prior Art Statement
A hydraulic amplifier arrangement is previously known in association with electronically controllable shock absorbers. A control of a restriction determines the damping effect which may be carried out with proportionately small control signals. Thus, a small mass can be used in the element for controlling the function, which means that the system can work with small inductances. Reference is made to patent application PCT/SE85/00120 (WO 85/04698), which relates to an arrangement which permits changes in the damping characteristic during one and the same piston stroke.
The known arrangements for such control require comparatively complicated control equipment, in the form of micro-computer equipment, for example, and the necessary software.
However, there is a requirement for applications in which the control function for the damping characteristics of the shock absorber can be simplified while maintaining high demands on the controllable damping function. It must be possible, for example, to obtain uniform damping effects within the entire adjustment range by the use of simple settings of a potentiometer, pressure in a suspension system, speed monitoring elements, injection pumps, etc. It should also be possible to carry out adjustments in a stepless manner, if it is so desired.
In another case it is desirable to be able by means of electronic control to vary the shock-absorbing capacity of the shock absorber. The variation shall in this case be capable of taking place at even high speed, which presupposes a high speed of data transmission from the control unit to the shock absorber, and accordingly the latter shall be capable, for example, of varying its shock-absorbing characteristic several times during one and the same piston stroke. The control unit may consist of a microcomputer, and the shock absorber can also operate with a feed back circuit, by a width parameter data (the position, speed and direction of movement, etc., of the piston) are fed back to the control unit to be utilized in its control of the shock absorber.
In addition, there is a requirement that it is possible to give the shock absorber a simple and reliable construction. It must not be possible, for example, for variations in existing parameters, such as the piston speed, to influence the set damping characteristic. It must also be possible for the arrangement to function with small controls and weak control signals, i.e. with an amplifier/servo function.